The technique of writing digital data on optical disk media began to popularize when CD-Rs became popular. After that, DVD-Rs, DVD-RWs, DVD-RAMs and other optical disk media that have bigger storage capacities than CD-Rs have also become increasingly popular these days. A CD-R has a transparent substrate with a thickness of 1.2 mm and a storage layer supported on that transparent substrate. On the other hand, a DVD includes two transparent substrates with a thickness of 0.6 mm apiece and a storage layer sandwiched between those two transparent substrates. These storage layers store various types of digital data including image data, audio data, text data and programs and include either a dye or a phase change material.
As those various optical disk media have become increasingly popular, it has become more and more necessary to record index information or any other type of information, which allows the user to recognize the type of data stored on an optical disk medium easily, on the optical disk medium as visible information that is directly visible to him or her. To meet such a demand, printers for recording the visible information by printing letters or pictures on the label side of an optical disk medium are available. However, such a printer should be prepared separately from the optical disk drive, and therefore, would force the user to pay an extra cost. Also, generally speaking, a printer is put on sale as a peripheral device for a personal computer. That is why to print a label on a DVD on which some data has been written by a DVD recorder, a personal computer should be started and then the DVD should be put in place in the printer, thus causing the user extra time and trouble.
Patent Document No. 1 discloses an optical disk medium with a thermal layer for label printing and an optical disk drive for directly recording visible information on that thermal layer. The optical disk medium includes a protective substrate, a dye recording layer, a reflective layer, a protective layer, a thermal layer and a protective coating, which are stacked in this order. In recording visible information on the thermal layer using this optical disk drive, the optical disk medium is inserted into the optical disk drive such that the thermal layer faces an optical pickup device. Then, the optical disk drive irradiates the thermal layer with a laser beam, thereby recording visible information on the thermal layer. To determine whether the layer of the given optical disk medium that is facing the optical pickup device is the dye recording layer or the thermal layer, it may be determined whether or not ATIP (absolute time in pregroove) information is detected when the given optical disk medium is accessed. If NO ATIP information is detected, then it can be determined that the optical pickup device is now facing the thermal layer.                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2003-203348        